Parasitic extrinsic collector resistance (Rcx) can significantly limit the performance of high-performance bipolar or bipolar and complementary metal-oxide-semiconductor (BiCMOS) devices such as silicon-germanium (SiGe) Heterojunction Bipolar Transistors (HBTs). In an attempt to limit Rcx in a SiGe HBT or other device, a highly-doped N-type (N+) buried layer in conjunction with an epitaxial silicon layer has conventionally been used to form a very low resistance region below the surface of the SiGe HBT or other device, thereby reducing the lateral component of Rcx. This conventional buried layer/epitaxial layer approach is described in more detail in U.S. Pat. No. 5,061,646, which patent is hereby incorporated herein by reference.
Due to the depth and thickness of the N+ buried layers used, the addition of deep trench isolation structures to the SiGe HBT or other device is typically required in order to limit the parasitic collector-substrate capacitance of the SiGe HBT or other device to acceptable levels. Therefore, the conventional buried layer approach used to limit Rcx can add considerable complexity and expense to the overall manufacturing process of the SiGe HBT or other device. Accordingly, a need exists for a method of limiting Rcx in a SiGe HBT or other device without requiring the expense and complexity necessitated by a conventional buried layer.
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The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner.